1. Field of the Invention
The present invention relates to a vehicle load control system suitable for use in controlling electric power fed to lamps and motors aboard a vehicle.
2. Related Art
In a common vehicle, various loads such as lamps and motors are distributed throughout a vehicle body, and control switches for activating the loads are disposed around a driver's seat. The control switches and the loads which correspond to the control switches are connected together by signal lines. Recent vehicles are provided with a larger number of loads, and hence the number of signal lines is also increased. As a result, a wire harness (WH) which ties the signal lines and power lines in a bundle becomes larger in diameter and weight. This, in turn, makes it very laborious to lay the wire harness in the vehicle body, as well as resulting in the heavier vehicle body.
To prevent the above problem, a multiplex communications system is conventionally proposed, as shown in FIG. 37. In this system, the control switches disposed around the driver's seat are intensively connected to one unit A provided in the vicinity of the driver's seat. The loads distributed throughout the vehicle body are intensively connected to, for example, one unit B disposed in the vehicle body. These units A and B are connected to each other through a multiplex transmission line L.
In that multiplex communications system, control switches SW.sub.1 -SW.sub.n such as switches and volumes are connected to the unit A which acts as a control signal multiplex-processing section. On the other hand, loads LR.sub.1 -LR.sub.n which are arbitrarily activated by the control switches SW.sub.1 to SW.sub.n are connected to the unit B which acts as a load control section. The units A and B are connected to each other through a multiplex transmission line L. Control signals generated as a result of the operation of the control switches SW.sub.1 -SW.sub.n are combined into a single signal by time-division multiplexing. The thus multiplexed signal is then sent to the unit B over the multiplex transmission line L, and the unit B then separates the multiplexed signal into the original control signals. By means of these control signals, the electric power fed to the corresponding loads LR.sub.1 -LR.sub.n is controlled. The means for connecting the units A and B to each other is standardized by the multiplex transmission line L. Hence, even if the control switches SW.sub.1 to SW.sub.n and the loads LR.sub.1 and LR.sub.n are changed, it is not necessary to change the connecting means. In consequence, the number of wire harness to be laid in order to connect the control switches with the load is considerably reduced.
Recently, associated with an increase in the number of on-vehicle systems and improvements in the performance of them, the number of, and the number of types of, control switches related to the on-vehicle systems are increasing. Further, the positions of the control switches which are many in number and have a lot of types also change as the number of types of vehicle specification increases. Even in such a circumstance, the use of the multiplex transmission line makes it possible to standardize inter-unit wire harness for each type of vehicle specification.
The loads are not simply turned on and off by the actuation of the control switches SW.sub.1 -SW.sub.n. For example, there are several types of lamp; namely, a lamp which constantly illuminates in response to the actuation of the control switch, a lamp which blinks by the actuation of the control switch, and a lamp which does not immediately illuminate by turning on the control switch, such as a lamp used in a bus which illuminates constantly or blinks corresponding to the opening/closing action of the door. If the lamps are changed according to the vehicle specifications, it is necessary to change the unit A which acts as the control signal multiplex processing section and the unit B which acts as the load control section, for each change. The diversification of parts results in increased manufacturing cost as well as the troublesome management of the parts.
Further, the wire harness laid between the control switches SW.sub.1 to SW.sub.n and the unit A in order to connect them together becomes complicated, or the number of types of wire harness increases. Further, the ease of connection of the wire harness to the switches is deteriorated, which in turn adds to the manufacturing cost.